GlrawTextureLoader cannot load texture with file suffixes

When converting "gloperate-logo.png" into a glraw texture, the default output name was "gloperate-logo.501.168.rgba.ub.glraw". This file could not be loaded with GlrawTextureLoader, propably because the detected suffix contains more than just ".glraw".

Fix GlrawTextureLoader to accept all ".glraw" and ".raw" files, regardless of how many periods the filename may include.

Start at the GlrawTextureLoader entry point and reproduce the failure using gloperate-logo.501.168.rgba.ub.glraw. Check loading behavior for filenames containing multiple periods and for both .glraw and .raw suffixes; done means all such files load successfully.

Written by the indexing model from the issue text.